Neptune CFD : Diphasic Simulation

For diphasic simulation, minor modifications are required in edamox compared to monophasic simulation. Simulations were launched by imposing a heat flux ranges between 2000 - 30000 W/m2 as demanded by Technip. 

The special module - ‘water and steam’ was selected for liquid - gas phase simulation.

Figure 17: Neptune Special Modules panel for nucleate boiling

In the ‘fluid & flow prop’ windows, the setting remains very similar to the single phase simulation. Number of phases should be set automatically to 2, with phase 1 considered as liquid and phase 2 as gas phase by default. No turbulence models were selected as turbulence was not expected. It is remarkable that there is a new windows ‘INTER-PHASE FORCES’ to define the different inter-phase forces (Figure 18). The bubbly flow is likely to be produced for the heat fluxes range, therefore the following laws were considered for the simulations:

Figure 18: Neptune Fluid&Flow props panel, definition of interphase forces for nucleate boiling

In the ‘Generalities’ panel, the ‘CATHARE functions’ option is selected by default. CATHARE functions are predefined to model H20 and Freon 12 properties. Hence, the option has to be deselected and propane properties such as superficial tension and latent heat have to be defined in USPHY.F.

Besides, the nucleate boiling option was chosen as wall transfer model. The wall temperature and different heat fluxes were calculated by PREVAP.F and ALGO_EV.F. In the ‘Boiling Parameters’ corner, there are two models, 3-flux model (known as GRE model) and 4-flux model (developed by EDF), proposed for fluid/wall heat transfer model. The 4-flux model is developed for higher heat flux, close to critical heat flux by taking into account the contribution by convection of the gas phase to the total heat flux.The detail of these two models can be found in ‘Bibliographic research’ section. The ‘Solid Wall properties’ was deactivated because there was no wall thickness to take into consideration. 

Figure 19:Neptune Generalities panel for nucleate boiling

Two scalars were defined in ‘Scalars’ module for liquid phase and gas phase and the wall boundary condition was modified accordingly.

In order to access the wall temperature and different heat fluxes for data analysis, User arrays can be defined in ‘Input-Output Control – USER’ panel and modifications have to be made in PREVAP.F to register the interesting parameters in all the cells. 6 users were registered to access :

  • TW = Wall temperature
  • PHI = Total heat flux,
  • PHIC = Monophasic convective heat flux in the liquid phase
  • PHIC2 = Convective heat transfer between the wall and the vapour phase,
  • PHIQ = Transient conductive heat flux, called quenching heat flux,
  • PHIE = Vaporization heat flux.